1. Field
The present invention relates generally to sound barriers and more specifically to a system for absorbing sound waves emanating in particular from highways, railroads, and similar transportation systems.
2. Prior Art
Since the advent of complex motorized transportation systems, such as railroads, automobiles and airplanes, there has been a need to reduce or prevent noise caused by such systems from effecting surrounding neighborhoods and businesses. Consequently, a number of devices and systems have been created which have been somewhat effective in alternating such noise.
Common barriers such as fences constructed of wood or a similar lightweight material probably served as the first noise barriers. While effective in preventing sight access, such barriers are quite ineffective in preventing the transmission of sound waves.
Concrete or masonry barriers and barriers constructed of a similar heavy material are perhaps more commonly used in attempting to prevent noise transmission. Barriers constructed of concrete are far superior to wood structures in accomplishing this goal, and yet it has been determined that concrete barriers and the like tend more to deflect sound waves rather than to dampen or absorb the same. Hence, while these types of barriers seem to be suitable for the accomplishment of some tasks along a highway or railroad track, they leave much to be desired in the area of preventing sound wave transmission.
Lately, much experimentation has been done with barriers having extruded members, particularly those which are modularly connected together, some of which are constructed of thermoplastic materials which absorb rather than deflect sound waves. Such structures may be effective in dampening much of the noise generated by highway traffic, locomotives, airplanes, and the like, although these barriers are not as effective as desirable. Furthermore, many of these barriers are constructed of materials which break down quickly or lose their resiliency when subjected to adverse conditions such as extreme weather and high-velocity impacts with foreign objects.
U.S. Pat. No. 3,948,009 discloses a sound insulating wall which is made from a composite of rubber shavings having a size within the range of 1 to 20 cubic centimeters incorporated with a binder of reactive resin. This composite is formed into a board which can be inserted at its ends into a pair of vertical supports. These boards are designed for improved absorption of sound by providing full exposure of the composite to the sound environment. Strength for the boards is supplied by increasing the board thickness or by reinforcing the interior of the board with wire (col 5, line 10) or other mechanical inserts.
Unfortunately, the nature of the composite of tire shavings and binder makes the board vulnerable to vandalism and breakage due to impact. Because its surface is substantially exposed, vandals can readily cut and tear away the aggregate structure. Furthermore, the structural weakness of the composite results in breakage on impact, even when reinforced internally. The extensive surface exposure also invites degradation by the elements, based on a tendency of the composite to flake and separate. Although, there is advantage over the prior art sound wall structure, this patent teaches the need to go to the extreme construction wherein sound absorbing properties of the material dictate the choice of a soft surface construction which is vulnerable to wear and failure.
What is needed is an improved sound absorbing wall which offers the strength of earlier constructions such as wood and metal, but which also incorporates the requirement of absorption of sound, rather than merely sound reflection. Such a system would advantageously be resilient and capable of surviving modest impacts, and also be capable of some structural support functions as well as provided the maximum sound absorption of a soft rubber surface.